The present invention relates to an image processing apparatus for compressing and processing image data output from an image reading means, and is suitable for use to improve the functionality of digital copying apparatuses, facsimile apparatuses and the like.
In digital copying apparatuses, for example, memory copy mode is known, wherein image data read from a document are temporarily stored in memory, and a copy image is printed based on said stored image data. Thus, a document is read once regardless of the number of copies to be made when making a plurality of copies in memory copy mode. When the document reading speed is slower than the printing speed, therefore, the copying time can be greatly reduced by using the memory copy mode. Electronic sorting is an example of a memory copy mode application. Electronic sorting is a copy mode wherein image data read from a plurality of original documents are stored in memory, and the image data of each document are repeatedly read out from said memory and copies of a plurality of documents are sequentially made one by one. Normally, compressed image data (hereinafter referred to as "compressed data") are stored in memory so as to allow the storage of as many documents as possible.
In conventional copying apparatuses, image data in pixel units obtained by scanning a document are stored in pixel array sequence in an image memory, a compression process starts after waiting for the image data of one page, i.e., image data corresponding to one document page, to be stored. That is, after one page of a document has been read, the process of compressing the obtained image data is started. Scanning of the next document page is accomplished after the compression processing of the previous one page is completed. In other words, after the compression processing of the image data of the read document completes, the reading of the next document begins.